Tire with carcass ply rubber composition

ABSTRACT

The present invention relates to a tire with a carcass ply component having a rubber composition of relatively low carbon black content with the carbon black having a defined structure and particle size.

FIELD

This invention relates to a tire having a carcass ply component with arubber composition having a low carbon black content where the carbonblack is of a defined structure and particle size.

BACKGROUND OF THE INVENTION

Pneumatic rubber tires are conventionally prepared with a rubber treadand supporting carcass. The carcass is conventionally composed of one ormore rubberized cord reinforced plies. Such construction is well knownto those having skill in such art.

Here, it is desired to provide such rubber composition which contains arelatively small amount of carbon black reinforcement on the order ofabout 15 to about 35 phr and in the absence, or at least substantialabsence, of silica and accompanying silica coupling agent.

It is recognized that in U.S. Pat. No. 5,396,940 a carcass ply rubbercomposition has been disclosed which is composed of 5-95 phr ofepoxidized natural rubber, 5-85 phr of silica, a silica coupler, carbonblack which can be a carbon black such as N299, which can also contain95-5 phr of other rubbers including natural rubber and cis1,4-polybutadiene rubber.

In the description of this invention, the term “phr” where used means“parts of material by weight per 100 parts by weight of rubber”.

SUMMARY AND PRACTICE OF THE INVENTION

In accordance with this invention a tire comprised of a tread andsupporting carcass wherein said carcass contains at least one plycomprised of a cord reinforced rubber composition and wherein saidcarcass ply rubber composition is comprised of, based on 100 phr ofrubber, (A) about 60 to about 90 phr of natural cis 1,4-polyisoprenerubber and about 10 to about 40 phr of cis 1,4-polybutadiene rubber, (B)about 15 to about 35, alternatively about 20 to about 30, phr of carbonblack having a D B P value in a range of about 110 to about 135 cm³/100g and an Iodine adsorption value in a range of about 90 to about 120g/kg, and (C) about 2 to about 8 phr of rosin acid.

In practice, the rubber composition for the carcass ply is oftenreferred to as a ply coat.

Conventionally, the carcass ply component of the tire is a cordreinforced element of the tire carcass. Often two or more carcass plycomponents are used in a tire carcass. The carcass ply component itselfis conventionally a multiple cord reinforced component where the cordsare embedded in a rubber composition which is usually referred to as aply coat. The ply coat rubber composition is conventionally applied bycalendering the rubber onto the multiplicity of cords as they pass over,around and through relatively large, heated, rotating, metal cylindricalrolls. Such carcass ply component of a tire, as well as the calenderingmethod of applying the rubber composition ply coat, are well known tothose having skill in such art.

The importance of using a relatively low level of carbon blackreinforcement for the ply coat, is to endeavor to achieve a high reboundvalue and relatively low hysteresis for the rubber composition which isintended, ultimately, to enhance (reduce) the tire's rolling resistance.Because a relatively small amount of carbon black reinforcement is to beused, it was decided to try a higher than normal structured (higherreinforcing) carbon black than what might be used for a carcass plyrubber, more of the type of rubber which might be used for a tire treadrubber composition.

The importance of using natural rubber for the ply coat is to endeavorto obtain a relatively high shear strength, low hysteresis and goodprocessability during the calendering of the ply coat onto the cordreinforcement.

It is desired to use cis 1,4-polybutadiene rubber as an elastomer in theply coat rubber composition to contribute to a relatively low hysteresisand improved compound aging.

The importance of using rosin acid for the ply coat rubber compositionis to endeavor to achieve good cured adhesion to the ply cords whilemaintaining good, original and aged tack. Various rosin acids can beused, particularly natural occurring rosin acids, although they might berefined somewhat. Representative of such rosin acids are, for example,wood rosin, tall oil rosin and gum rosin. Such rosin acids and their usein rubber compositions are well known to those having skill in such art.

In a practice of this invention, it is preferred that the rosin acid isutilized in place of more conventional phenolic resin which are morecommonly used for enhancing tack for a rubber composition. This isbecause, for the purposes of this invention, it is considered hereinthat such the phenolic resins would provide the necessary building tackbut have been observed to cause a reduction in cord adhesion.

For the practice of this invention, it is intended to not use silicareinforcement, at least not any substantial amount of silica, (10 phr or5 phr or less and preferably zero amount) since it is desired, for thisinvention, that the amount of reinforcing filler, including thespecified carbon black, be kept relatively low. Therefore, a greaterreinforcing effect of the carbon black, particularly a relatively highstructure carbon black is desired to offset the use of a relativelysmall amount of carbon black.

It is also intended to not use epoxidized natural rubber for the plycoat rubber composition because it is envisioned that such rubber wouldtend to cause an unwanted higher hysteresis for the ply coat rubbercomposition.

Accordingly, for the practice of this invention, it is preferred thatthe carcass ply rubber composition is exclusive of any appreciableamount, particularly of any amount of (1) epoxidized natural rubber, (2)phenolic, particularly synthetic phenolic, tackifiers, (3) silica, (4)silica coupler and/or (5) additional carbon black having a D B P valueof less than 100 cm³/100 g and Iodine No. value of less than 90 g/kg.

If desired, up to about 10, such as about 5 to about 10, phr ofadditional rubber may be included in the ply coat rubber compositionselected from at least one of medium vinyl polybutadiene rubber (40-60percent vinyl), styrene-butadiene rubber, styrene-isoprene rubber andstyrene-isoprene-butadiene rubber.

The D B P and Iodine value characterizations of carbon black are wellknown and a reference to such values relating to carbon black and ASTMmethods of their determination may be found in The Vanderbilt RubberHandbook, 13^(th) edition (1990), pages 416-419.

In general, the D B P value tends to relate to what is known as thestructure of the carbon black. Relatively high structure carbon blacksare typically used for reinforcing tire tread rubber compositions suchas those having a D B P (dibutylphthalate) value in a range of about 100to about 160 cm³/100 g. Carcass ply rubber compositions usually use alower structure carbon black reinforcement such as those having a D B Pvalue in a range of about 80 to about 100 cm³/100 g.

Significantly, for the purposes of this invention a relatively low levelof carbon black is used for the carcass ply rubber composition in orderto endeavor to achieve higher rebound and reduced hysteresis. Therefore,it is envisioned herein that a higher structure carbon black with a D BP value in a range of about 110 to about 135 cm³/100 g be used in orderto provide enough reinforcement.

Further, it is desired to use a carbon black reinforcement with a finerparticle size than what may normally be used for a carcass ply rubbercomposition as indicated by the carbon black's Iodine No. value which,in turn, is a surface area indicator.

Significantly, carbon blacks used for carcass ply reinforcement areusually of a relatively large particle size characterized by having anIodine No. value in a range of about 30 to about 60 g/kg, whereassmaller carbon blacks are often used for tread rubber usually having aIodine No. value in a range of about 80 to about 140 g/kg.

For this invention, it is envisioned that a smaller than typical carcassply carbon black be used with an Iodine Number value in a range of about90 to about 120 g/kg.

In practice, cords of various compositions may be used for the carcassply such as, for example, but not intended to be limiting polyester,aramid and nylon. Such cords and their construction, whethermonofilament or as twisted filaments, are well known to those havingskill in such art.

It is recognized that conventional compounding ingredients may be usedin the preparation of the ply coat rubber composition. The ply coat, inthe finished tire is sulfur cured as a component of the tire. Forexample, the sulfur cured ply coat rubber composition may containconventional additives including reinforcing agents, fillers, peptizingagents, pigments, stearic acid, accelerators, sulfur vulcanizing agents,antiozonants, antioxidants, processing oils, activators, initiators,plasticizers, waxes, pre-vulcanization inhibitors, extender oils and thelike. Representative of conventional accelerators may be, for example,amines, guanidines, thioureas, thiols, thiurams, sulfenamides,dithiocarbamates and xanthates which are typically added in amounts offrom about 0.2 to about 3 phr. Representative of sulfur vulcanizingagents include element sulfur (free sulfur) or sulfur donatingvulcanizing agents, for example, an amine disulfide, polymericpolysulfide or sulfur olefin adducts. The amount of sulfur vulcanizingagent will vary depending on the type of rubber and particular type ofsulfur vulcanizing agent but generally range from about 0.1 phr to about3 phr with a range of from about 0.5 phr to about 2 phr being preferred.Representative of the antidegradants which may be in the rubbercomposition include monophenols, bisphenols, thiobisphenols,polyphenols, hydroquinone derivatives, phosphites, phosphate blends,thioesters, naphthylamines, diphenol amines as well as other diarylamine derivatives, para-phenylene diamines, quinolines and blendedamines. Antidegradants are generally used in an amount ranging fromabout 0.1 phr to about 10 phr with a range of from about 2 to 6 phrbeing preferred. Amine based antidegradants, however, are not preferredin the practice of this invention. Representative of a peptizing agentthat may be used is pentachlorophenol which may be used in an amountranging from about 0.1 phr to 0.4 phr with a range of from about 0.2 to0.3 phr being preferred. Representative of processing oils which may beused in the rubber composition of the present invention include, forexample aliphatic, naphthenic and aromatic oils. The processing oils maybe used in a conventional amount ranging from about 0 to about 30 phrwith a range of from about 5 to about 15 phr being more usuallypreferred. Initiators are generally used in a conventional amountranging from about 1 to 4 phr with a range of from about 2 to 3 phrbeing preferred.

Accelerators may be used in a conventional amount. In cases where only aprimary accelerator is used, the amounts range from about 0.5 to about 2phr. In cases where combinations of two or more accelerators are used,the primary accelerator is generally used in amounts ranging from 0.5 to1.5 phr and a secondary accelerator is used in amounts ranging fromabout 0.1 to 0.5 phr. Combinations of accelerators have been known toproduce a synergistic effect. Suitable types of conventionalaccelerators are amines, disulfides, guanidines, thioureas, thiazoles,thiurams, sulfenamides, dithiocarbamates and xanthates. Preferably, theprimary accelerator is a sulfenamide. If a secondary accelerator isused, it is preferably a guanidine, dithiocarbamate or thiuram compound.

Pneumatic tires are conventionally comprised of a generally toroidalshaped carcass with an outer circumferential tread adapted to the groundcontacting space beads and sidewalls extending radially from andconnecting said tread to said beads. The tread may be built, shaped,molded and cured by various methods which will be readily apparent tothose skilled in the art.

The sulfur cured ply rubber composition of the present invention may beintegral with and adhere to various tire carcass substrate rubbercompositions.

The practice of this invention is further illustrated by reference tothe following examples which are intended to be representative ratherthan restrictive of the scope of the invention. Unless otherwiseindicated, all parts and percentages are by weight.

EXAMPLE

Rubber compositions containing the materials set out in Table 1 wereprepared in a B R Banbury using three separate stages of addition,namely a non-productive mixing stage for a total of about 4 minutes to atemperature of about 160° C. followed by a productive mixing stage forabout 2 minutes to a temperature of about 105° C. where the sulfur andcuratives were added. The terms “non-productive” and “productive” asused for mixing stages for mixing rubber compositions are well known tothose having skill in such art.

The following Table 1 illustrates the rubber compositions withcomposition A representing a control (Ctrl A); compositions B and Crepresenting additional sample preparations (Exp B and Exp C) andexperimental composition D (Exp D) is representative of a composition ofthis invention.

TABLE 1 Material Ctrl A Exp B Exp C Exp D Productive Mix Stage Naturalrubber¹ 70 70 70 70 Cis 1,4-polybutadiene² 0 30 30 30 Emulsion SBR³ 30 00 0 Carbon black, N660 60 0 0 0 Carbon black, N299 0 28 28 28 Processingoil⁴ 14.9 10 10 10 Phenolic tackifier⁵ 3.5 4.0 0 0 Rosin acid⁶ 0 0 0 4Productive Mix Stage Zinc oxide 2 2 2 2 Sulfur 2.1 2.4 2.4 2.4Sulfenamide 1.6 1.8 1.8 1.8 Accelerator(s) ¹Cis 1,4-polyisoprene.²Obtained as BUDENE ® 1208 from The Goodyear Tire & Rubber Company.³Obtained as PLF 1778 from The Goodyear Tire & Rubber Company-contains37.5 phr naphthalene/paraffinic processing oil and 23.5 percent styrenewith a Mooney viscosity (ML1 + 4) of about 50. It is reported in Table 1on a dry weight basis. ⁴Additional naphthenic/paraffinic rubberprocessing oil. ⁵Obtained as SP-1068 from the Schenectedly ChemicalCompany. ⁶A natural water white Chinese gum rosin obtained from theHarwick company.

The rubber compositions were cured for about 18 minutes to a temperatureof about 150° C. The physical properties of the rubber compositions areshown in the following Table 2.

TABLE 2 Ctrl Exp Exp Exp Material A B C D Rheometer, 170° C. MaximumTorque (MPa) 30.3 33.8 36.8 31.0 Minimum Torque (MPa) 5.5 6.2 7.0 5.5T₉₀, minutes 2.9 2.8 2.8 3.3 Stress-Strain Tensile, Mpa 17.0 15.6 14.615.4 Elongation at Break, % 525 577 490 591 300% Modulus, MPa 8.7 5.26.6 4.9 Hardness, Shore A 100° C. 50 46 58 46 Rebound 100° C. 68 74 7773 Peel Adhesion (Tear)¹ Newtons 89 67 60 81 Tack (MPa) Original 10 16 917 Aged 7 days at 23° C. 20 21 2 20 Adhesion to Polyester Cord¹ Newtons116 88 110 129 Percent Coverage 100 70 100 100 Pierced Groove Flex120/180/240 minutes, Fail 1.6/ 1.3/ F/— 0.54/ or inches of crack growthF/— F/— /— 1.4/F ¹The peel adhesion and cord adhesion tests aredescribed in U.S. Pat. No. 5,328,963.

These results show that the natural rubber/polybutadiene rubber ply coatrubber composition with a relatively low level of defined carbon black(28 phr) together with a rosin acid, represented by Exp D, demonstratedgood tack which is useful in tire building, high cord adhesion usefulfor tire component durability and a desirable high rebound value usefulfor enhancing a tire's rolling resistance.

The results further indicate that the Exp D sample had the best flexfatigue resistance according to the Groove Flex test which is consideredherein to be a beneficial value for a tire tread rubber composition.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

What is claimed is:
 1. A tire comprised of a tread and supportingcarcass wherein said carcass contains at least one carcass ply comprisedof a cord reinforced rubber composition, wherein said cord is composedof a monofilament or of twisted filaments and wherein said cordreinforced rubber composition is comprised of, based on 100 phr ofrubber, (A) rubber consisting essentially of about 60 to about 90 phr ofnatural cis 1,4-polyisoprene rubber about 10 to about 40 phr of cis1,4-polybutadiene rubber wherein said cis 1,4-polybutadiene rubberconsists of cis 1,4-polybutadiene rubber, and up to about 10 phr of atleast one rubber selected from medium vinyl polybutadiene rubber (40 to60 percent vinyl), styrene-butadiene rubber, styrene-isoprene rubberand/or styrene-isoprene-butadiene rubber, (B) about 15 to about 35 phrof carbon black having a D B P value in a range of about 100 to about130 cm³/100 g and an Iodine adsorption value in a range of about 90 toabout 120 g/kg, and (C) about 2 to about 8 phr of tack and adhesionenhancing rosin acid; wherein said rosin acid is a natural rosin acidselected from at least one of wood rosin, tall oil rosin and gum rosin,and wherein said cord reinforced rubber composition is exclusive of anyappreciable amount of epoxidized natural rubber, phenolic tackifier andsilica.
 2. The tire of claim 1 wherein said carcass ply rubber,composition is exclusive of any appreciable amount of phenolictackifiers.
 3. The tire of claim 1 wherein said carcass ply rubbercomposition is exclusive of any appreciable amount of silica and silicacoupler.
 4. The tire of claim 1 wherein said carcass ply rubbercomposition is exclusive of any appreciable amount of carbon blackreinforcement having a D B P value less than 110 cm³/100 g and an IodineNo. value of less than 90 g/kg.
 5. The tire of claim 1 wherein saidcarcass ply rubber composition exclusive of any appreciable amount ofphenolic tackifier, silica and carbon black reinforcement having a D B Pvalue of less than 110 cm³/100 g and Iodine Number value of less than 90g/kg and where said rosin acid is selected from at least one of woodrosin, tall oil rosin and gum rosin.
 6. The tire of claim 5 wherein saidcord reinforcement for said carcass ply is selected from at least one ofpolyester, aramid and nylon cords.
 7. The tire of claim 1 wherein saidcord reinforcement for said carcass ply is selected from at least one ofpolyester, aramid and nylon cords.
 8. The tire of claim 1 wherein saidcarcass ply rubber composition contains from about 5 to about 10 phr ofat least one additional elastomer selected from at least one of mediumvinyl polybutadiene rubber (40 to 60 percent vinyl), styrene/butadienerubber, styrene/isoprene rubber and styrene/isoprene/butadiene rubber.9. The tire of claim 5 wherein said carcass ply rubber compositioncontains from about 5 to about 10 phr of at least one additionalelastomer selected from at least one of medium vinyl polybutadienerubber (40 to 60 percent vinyl), styrene/butadiene rubber,styrene/isoprene rubber and styrene/isoprene/butadiene rubber.
 10. Thetire of claim 1 wherein said carcass ply rubber composition containsabout 15 to about 30 phr of said carbon black and is exclusive ofphenolic tackifier, silica and carbon black reinforcement having a D B Pvalue of less than 110 cm³/100 g and Iodine Number value of less than 90g/kg.